1. Field of the Invention
This invention relates to a color television system including a video tape recorder (VTR) and a color television receiver, and more particularly to a color television system including a video tape recorder and a color television receiver which has an automatic control circuit for controlling color level and hue with a reference signal contained in a video signal.
2. Description of the Prior Art
For example, a color television system including a VTR and a color television receiver is known in which the reproduced signals of the VTR are modulated with a high frequency carrier signal for a specified idle television channel, for example, the second television channel in Tokyo, and the modulated signal are received by the color television receiver tuned to the second channel.
The following recording/reproducing method for increasing the recording density(record tracks per inch) is employed for the VTR of such a system:
As shown in FIG. 1, two rotary magnetic heads Ha and Hb are diametrically arranged in a tape guide drum 2. A magnetic tape 1 travels obliquely around a 180 degree portion of the tape guide drum 2, and during this travel around the tape guide drum 2, the magnetic tape 1 is contacted by the magnetic heads Ha and Hb. As shown in FIG. 2, gaps g.sub.a and g.sub.b of the magnetic heads Ha and Hb are different from each other in their inclination angle to the scanning direction shown by an arrow 3. The magnetic heads Ha and Hb rotate one revolution per one frame of video signals. In the recording, trace tracks Ta and Tb are alternately formed on the magnetic tape 1 by the magnetic heads Ha and Hb every field of the video signals, as shown in FIG. 3.
Referring to FIG. 4, in the recording operation, color video signals are applied through an input terminal 11 to a low pass filter 12 to obtain luminance signals. The luminance signals are applied to a frequency modulator 13. Thereby, modulated luminance signals having high frequency components within a recordable/reproducable frequency band are obtained, and applied to an adder 14.
The color video signals are applied also to a band pass filter 15. Chrominance signals whose subcarrier has a frequency fs, are obtained from the band pass filter 15, and applied to a frequency converter 16. Thereby, the frequency of the chrominance signals is converted to a low frequency.
An output of a switching circuit 17 is applied to the frequency converter 16. A signal having a frequency (fs+fa) is applied to one input terminal of the switching circuit 17, and another signal having a frequency (fs+fb) is applied to another input terminal of the switching circuit 17. The frequency (fs+fb) differs from the frequency (fs+fa) by half of a horizontal scanning frequency fh. The switching circuit 17 is changed over with a change-over signal Sc. In the fields when the magnetic head Ha contacts the magnetic tape 1, the switching circuit 17 is changed over to the signal of the frequency (fs+fa), as shown in FIG. 4, and the signal of the frequency (fs+fa) is applied to the frequency converter 16. And in the fields when the magnetic head Hb contacts the magnetic tape 1, the switching circuit 17 is changed over to the signal of the frequency (fs+fb), and the signal of the frequency (fs+fb) is applied to the frequency converter 16.
Accordingly, chrominance signals Ca in which the frequency of the subcarrier has been converted to a frequency fa, are obtained from the frequency converter 16 in the fields when the magnetic head Ha contacts the magnetic tape 1. And chrominance signals Cb in which the frequency of the subcarrier has been converted to a frequency fb, are obtained from the frequency converter 16 in the fields when the magnetic head Hb contacts the magnetic tape 1. The chrominance signals Ca and Cb are applied to the adder 14, and added to the modulated luminance signals thereby. The composite signals from the adder 14 are applied through an amplifier 18 to the magnetic head Ha and Hb. Thus, the chrominance signals Ca and Cb are recorded on the trace tracks Ta and Tb of the magnetic tape 1. As shown in FIG. 6A and Fig. 6B, the chrominance signals Ca and Cb are interleaved with each other in frequency components.
Referring to FIG. 5, in the reproducing operation, the signals from the magnetic heads Ha and Hb are applied through an amplifier 20 to a high pass filter 21. The modulated luminance signals are obtained from the high pass filter 21, and applied through a limiter 22 to a demodulator 23. The demodulated luminance signals from the demodulator 23 is applied to an adder 24.
When the magnetic head Ha scans not only the track Ta, but also a part of the adjacent track Tb, and when the magnetic head Hb scans not only the track Tb, but also a part of the adjacent track Ta, no cross-talk occurs, although so called "guard bands" are not formed between the adjacent tracks Ta and Tb in the recording operation. Because the modulated luminance signals are high frequency signals, luminance signals free of crosstalk are applied to the adder 24.
The reproduced signals from the magnetic heads Ha and Hb are applied through the amplifier 20 also to a low pass filter 25. The chrominance signals are obtained from the low pass filter 25. When the magnetic head Ha scans not only the track Ta, but also a part of the adjacent track Tb, the chrominance signals Cb interleaved with the chrominance signals Ca in frequency components are mixed as crosstalk components with the chrominance signals Ca in the chrominance signals from the filter 25, as shown in FIG. 6C, since guard bands are not formed between the adjacent tracks Ta and Tb in the recording operation. And when the magnetic head Hb scans not only the track Tb, but also a part of the adjacent track Ta, the chrominance signals Ca interleaved with the chrominance signals Cb in frequency components are mixed as crosstalk components with the chrominance signals Cb in the chrominance signals from the filter 25, as shown in FIG. 6D, since guard bands are not formed between the adjacent tracks Ta and Tb in the recording operation. The chrominance signals from the filter 25 are applied to a frequency converter 26. A switching circuit 27 is conneced to the frequency converter 26.
In the same manner as in the recording operation, the switching circuit 27 is changed over with a change-over signal Sc. In the fields when the magnetic head Ha contacts the magnetic tape 1, to reproduce the signals from the track Ta, the switching circuit 27 is changed over to the signal of the frequency (fs+fa), as shown in FIG. 5, and the signal of the frequency (fs+fa) is applied to the frequency converter 26. And in the fields when the magnetic head Hb contacts the magnetic tape 1 to reproduce the signals from the track Tb, the switching circuit 27 is changed over to the signal of the frequency (fs+fb), and the signal of the frequency (fs+fb) is applied to the frequency converter 26.
Accordingly, chrominance signals Csa in which the frequency of the subcarrier has been converted to the original frequency fs, are obtained from the frequency converter 26 in the fields when the magnetic head Ha contacts with the magnetic tape 1 to reproduce the signals from the track Ta, as shown in FIG. 6E. Crosstalk components interleaved with the chrominance signals Csa in frequency components are mixed with the chrominance signals Csa. And chrominance signals Csb in which the frequency of the subcarrier has been converted to the original frequency fs, are obtained from the frequency converter 26 in the fields when the magnetic head Hb contacts with the magnetic tape 1 to reproduce the signals from the track Tb, as shown in FIG. 6F. Crosstalk components interleaved with the chrominance signals Csb in frequency components are mixed with the chrominance signals Csb.
In order to remove the crosstalk components, the output signals of the frequency converter 26 are applied to a C-type comb line filter 28 which consists of a delay circuit 28b for delaying the output signals of the frequency converter 26 by a period of one horizontal scanning line, and a subtracter 28a. Thus, the original chrominance signals Cs without crosstalk component are obtained from the comb line filter 28, as shown in FIG. 6G, and applied to the adder 24 to be added to the luminance signals. The reproduced color video signals without crosstalk are obtained from an output terminal 29.
On the other hand, a VIR (vertical internal reference) signal for controlling hue and color level is contained in a color video signal transmitted from a broadcasting station. The VIR signal is contained in a 19-th horizontal scanning line section T.sub.19 of every vertical scanning line section, in the color video signal. The VIR signal contains, as a chrominance reference portion, a sine wave having the frequency 3.58 MHZ of the subcarrier, and the same phase as a burst signal. FIG. 7A shows signals contained in 18-th and 19-th horizontal scanning line sections. Horizontal synchronizing signals are denoted by P.sub.H, burst signals by Sb and the VIR signal by Sv. The burst signal Sb is at the black level, while the VIR signal Sv is at the color level corresponding to the standard brightness of the flesh color of human skin. Accordingly, when the chrominance signals are distorted in phase, the VIR signals Sb are similarly distorted in phase. The phase shifts of the VIR signals Sv from the burst signals Sb correspond to the phase distortions of the chrominance signals. Since the amplitudes of the VIR signals correspond to the levels of the chrominance signals, the former varies with the latter.
In the color television receiver, the VIR signals are picked up, from the 19-th horizontal scanning line section T.sub.19 of every vertical scanning line section to control the color level and hue. Thus, undistorted chrominance signals are obtained and so undistorted color pictures are reproduced on the screen of the color television receiver.
When the color video signals are reproduced in the VTR having the comb line filter in the reproducing circuit, the signals in the 19-th horizontal scanning line section are mixed with the signals in the 18-th horizontal scanning line section. When color bar signals are contained in the 18-th horizontal scanning line section T.sub.18, as shown in FIG. 7A, the VIR signals in the 19-th horizontal scanning line section T.sub.19 are mixed with the color bar signals in the section T.sub.18 by the comb line filter having the delay circuit for delaying the signals by the period of one horizontal scanning line section. Thus, the amplitude and phase of the VIR signals are distorted.
The signals contained in the horizontal scanning line section are added to the signals contained in the previous adjacent horizontal scanning line section, and the added signals are reduced to half in amplitude, by the comb line filter. When a pedestal level is maintained in the 18-th horizontal scanning line section T.sub.18 as shown in FIG. 7B, the amplitude of the VIR signal picked up from the 19-th horizontal scanning line section T.sub.19 is reduced to half by the comb line filter.
When the phase and level of the chrominance signals are controlled with the VIR signals thus distorted in phase and amplitude, in the color television receiver, the reproduced color picture is greatly distorted on the screen of the color television receiver. The desired color picture cannot be obtained.